Samples of the terrestrial cyanobacterium Nos toe commune Vaucher were collected at two different places in the vicinity of Würzburg, Germany, from August 1995 until November 1996 and analyzed for their pigment contents. Carotenoids, chlorophyll a, scytonemin and a mycosporine-like amino acid (MAA) were determined by high performance liquid chromatography or spectrophotometrically. Dry-weight related contents of chlorophyll a and carotenoids were minimal at the end of winter time and increased in May. The ratio between the carotenoids canthaxanthin and ß-carotene showed a positive correlation to irradiance in the warmer time of the year, but increased also in winter. Contents of the UV-A protective pigment scytonemin did not show any obvious response to the seasonal changes in radiation climate while contents of the UV-B protective pigment MAA increased during winter although UV-B irradiance was low at this time. It is concluded that other factors in addition to UV-B radiation mav induce MAA accumulation in N. commune under natural conditions